A packet switched data network such as the Internet can be considered to comprise a mass of nodes interconnected by data paths.
In packet switched data networks, monitoring a data path, or in other words, estimating a condition such as available bandwidth end-to-end over a data path of the network is useful in several contexts; including Service Level Agreement (SLA) verification, network monitoring and server selection.
Mainly, there are two ways to estimate a condition such as available bandwidth, namely passive or active monitoring.
Passive monitoring of available bandwidth of an end-to-end data path requires that all of the network nodes in the network path can be accessed, However, this is typically not possible. Therefore, measuring available end-to-end bandwidth is typically done by active probing of the data path. The available bandwidth can be estimated by transmitting probe traffic, such as User Data Protocol (UDP) probe packets including a train of probe packets into the data path, and then analyzing the observed effects of other data packet communications, here denoted, cross traffic on the probe packets. Typically, large UDP probe packets having a specified inter-packet separation are transmitted. This kind of active measurement requires access to both sender and receiver hosts, referred to as sender and receiver nodes, but does not require access to any intermediate node(s) in the path between the sender and receiver nodes. Conventional approaches to active probing require the transmission of probe packet traffic into the data path of interest at a rate that is sufficient transiently to use all available bandwidth and cause congestion. If only a small number of probe packets are used, then the induced transient congestion can be absorbed by buffer queues in the nodes. Accordingly, no data packet loss is caused, but rather only a small data path delay increase of a few data packets. The desired measure of the available bandwidth is determined based on the increase in delay due to the probe packets having experienced congestion between sender and receiver node. The probe packet rate where the data path delay begins increasing corresponds to the point of congestion, and thus is indicative of the available bandwidth. The estimation is typically produced by means of an analysis algorithm based on probe rate methods and are known per se. Examples of such algorithms that could be employed are: Bandwidth Available in Real Time (BART) presented in reference [1], pathChirp presented in reference [2], Pathload presented in reference [3] or Spruce presented in reference [4]. These are also described in a number of other prior art documents, such as U.S. Pat. No. 7,778,179 B2 (Ekelin et al) describing BART.
The current methods give an estimate of e.g. the available bandwidth for the whole network path between the sender and the receiver.
One problem with the existing active measurement methods is the time it takes to present the bandwidth estimate.
Further one problem is that the measured bandwidth estimate can give a higher capacity value than the capacity actual available.
Even with the Kalman filter the estimated bandwidth is showing bigger bandwidth than available, creating uncertainness to the measurements. This problem is discussed in ref. [1].